Concentration of minerals



Feb. 8, 1938. J, 1, DENNY ET AL, 2,107,289

CONCENTRATION OF MINERALS Filed OCb. 29, 1934 2 Sheets-Shedl l './Dm J.en/Vy. r/bw C aman Feb. 8, 1938. J. J. DENNY ET AL. 2,107,289

CONCENTRATION OF MINERALS Filed oct; 29, 1954 2 sheets-sheet 2 J0/729 len/7g. #ff/7 w" C. A@am m7.

Patented Fe, 8, '1938 UNITE-Di PATENT OFFICE CONCENTRATION 0F IWINERALSApplication October 29, 1934, Serial No. 750,442

10 Claims.

This invention relates to mineral concentra.-

tion and aims to improve mineral recovery and reduce concentrationcosts.

The4 nature of the invention may be readily 5 understood by reference toone embodiment illus tratevd in the accompanyingdrawings. f In saiddrawings: Fig. 1 is a plan view showing a grinding mill concentratingunit and classier in closed cirlO cuit, certain conventional'apparatusbeing shown diagrammatically to facilitate illustration;

Fig. 2 is a side elevation of the apparatus as viewed in the directionof the arrow 2 in Fig. 3;

Fig. 3 is an end view of the apparatus in the directi'on of the arrow 3in Fig. 1; and f Fig. 4' is an elevation, partly in section, of aflotation cell.

In concentrating minerals according to. the present invention, treatmentof the ore is under- 20 taken vwhile the mineral is in coarse conditionand as soon as a portion of the mineralis freed from the gangue. Inotherwcrds, the crushing or reduction of the ore is not carried to apoint where substantially all of the mineral isfree most of the mineral)but need be carried to a point where only a relatively smallfraction of`the mineral is free, before it is delivered to the concentrating unit.This procedure avoids both 30 the expense of unnecessary grinding of theore and (what is even more important) the production oi' a highpercentagey of very fine, unrecoverable mineral (slimes-which haveheretofore been the source of the greatest loss of mineral) which.

:35 is inevitable with continued grinding and regrinding. In priorpractices where the mineral has all been ground to substantially minusthree hundred twenty-five mesh, it has been necessary to recirculate theore through the grinding mill 40 from two to eight times, inevitablyresulting in the production of a large percentage of unrecoverableslimes and excessive mineral losses, notwithstanding the fact that about40% of such mineral may be recovered without further regrinding by animproved concentrating. unit. lPrior efforts to reduce the loss throughslimes have been far from successful.

As here shown, ore is delivered from the ore bins into grindingapparatus here represented by a ball-mill I and is there ground until afrac- 'tion of the mineralv is free, which-for purposes ofthe'illustrative process occurs when the ore will pass a one-quarterinch mesh screen. 'Ihe size of the ore generally varies from three tosix. mesh depending somewhat upon the specific gravy 2, (therebyresulting in an excessive pulverization ofA ity of the ore and thecharacter of the particles of ore. The percentage of material of coarsemesh will also vary with the character of the ore.

It will be understood that even when grinding ore to minus one-quarterinch mesh, a large per- 5 centage of it will be much iner. Neverthelessthe production of slimes is very substantially limited. A small4percentage of material in the form ofvv tramp iron,v broken balls,pieces of wood, etc. will exceed the limiting mesh size and for thatreason the discharge end Il .of themill is provided with a screen ortrammel I2 having a limiting size mesh screen'. The oversize materialYclis-l charges'at the open end I3 of the screenand is returned forregrinding asA presently described.gl5 Ground mineral of minusone-quarter inch (or Whatever the limiting size of the screen be) passesthrough the screen and into a launder I4 together with such water as isfed into the grinding mill. This amount is relatively small and`produces a concentrated pulp which in some instances may not besuiliciently dilute for treatment in the present concentrating unit, inwhich case additional water may be added at an appropriate point. Fromthe launder the pulp lpasses by gravity through the feed pipe I5 intothe concentrating unit (see particularly Fig. 4).

The concentrating unit is here illustrated in the form of a flotationunit which, as presently explained, may also function in cyanide andamalgamation processes mainly -as an agitator in which the -froth iseither incidental or absent. The illustrative notation unit is of thesubaeration type employing a gravity feed Aprinciple which eliminatesclogging of the apparatus 35 through accumulation of heavy sands in itsbottom. As will presently appear, the settling of heavy sands on theshut-down ofthe apparatus .will not clog the feed and prevent aresumption- 'of operation. vIn detail tlie flotation cell com- 40 prisesa boxlike container I6 adjacent the bottom of which is supported arotary impeller I'l ,which serves to effect a thorough mixing of therpulp with air (aeration of the pulp). 'I 'he impeller is in the presentcase supported from above by a rotary drive shaft I8 providedwithappropriate vertically adjusted thrust bearings I9 which carry theWeight of the shaft and the impeller and permit appropriate verticaladjustment of the latter when required by ensuing wear. ,The drive inthis instance is from motor '20 through one or more V-belts 2| to pulley22 on shaft |18. 'I'he motor bearings etc. are carried by an appropriatesubstructure 23 mounted upon the cell.v Sui"- rounding shaft I8 andextending from a point 55 limpeller to prevent free access thereto ofthe pulp in the upper portion of the cell and relieving the impeller ofthe load of such pulp.

The impeller is here shown in the form of a circular plate 26 having onits upper face a plurality of radial varies 2l (four in the presentinstance). In .the present instancel the impeller is also provided onits lower face with a plurality of tapered vanes 28 which graduallytaper down toward the edge of the plate. The impeller may advantageouslyhave rubber wearing surfaces since these are much better able towithstand the abrasive action of the pulp than is metal and greatlyoutlives metal impellers.

The pulp is fed to the impeller through the conduit'29 which leads fromthe pipe I5 to the sleeve 24 at a point above the impeller and therebydischarges thevpulp by gravity upon the impeller where it is intimatelymixed with the air and the combined pulp and air thrown outwardly andthence upwardly by the centrifugal action of the impeller. The vanes 21Yare preferably adjusted so as to provide a substantialclearance` 30below the hood 25 so as 'to increase the violence of agitation of pulpand air by causing the pulp to cascade over the successive veins andtherebyv secure a more eillcient incorporation of the air in the pulp.Submerged vertical baffles 3| prevent swirling action of the pulp whichmight disturb the quiet zone infthe upper portion of the ycell andthefroth layer, without however interfering with the velocity of the risingcurrentsof pulpi The .froth carrying the mineral concentrate dischargesthe froth lip 32 into launder 33. A rotating paddle wheel 34 isadvantageously pro-` vided to assist in discharge of froth. The mineralconcentrate in lamder 33 may be delivered either to storage or 'tosubsequent treatment by cyanidatlon, amalgamation,f etc. If for specialreasons the grade of the concentrate may advantageously be improved. itmay bev reground and refined or cleaned by further flotation. Generallyfurther reilnement is undesirable since the concentrateoriginallyrecovered is of sufllciently high grade that it cannot economically befurther reilne'd by regrinding and refltation.

The tailings discharge over a vertically adjustable Weir 35 (which isbelow the froth'level) into a launder 3B by which they are conducted tothe classifier` 3l in closed circuit with the grinding mill l0. i

The classifier here shown is of a mechanical type such as a conventionalDorr classifier. Its

' detalls are well known and need not be described hereexcept to notethat its function is to return heavy sands to the grinding mill andallow finely ground gangue andmineral to overflow at the overflow 38 fordelivery generally to batteries of notation machines. The pitch of thebottom `of the classifier as well as the speed of the rakes largelydetermine the flneness of a given ore which passes over the overflow. Inthis connection it is well to note that the mineral which is generallymuch heavier than the gangue (such as silica) will not be carried overthe'classifier overflow until it is much' more ilnely ground than thegangue. This characteristic of classifier operation materiallycontributes to excessive/grind-l ing of free mineral and productionof'slimes.

While attempts have heretofore been made to minimize regrinding of freedminerals by the interposition of a shaking table (Wilfley table) inclosed circuit with a classifier and grinding mill, this has not beenentirely successful and its use is not general. The principle ofoperation of the shaking table does not result in the removal of largeparticles of mineral which because of their flaky condition or largearea (as compared with volume) prevents their discharge with mineralconcentrate. Such large mineral particles although readily iloatable andrecoverable in the present flotation machine, are discharged by a tableas middlings or tailings to be unnecessarily reground.

It is evident from the foregoing that the operation of the grinding millclassifier and unit flotation cell in closed circuit results in theremoval of the mineral as and when it is free without the necessity ofregrinding. The oversize particles of mineral which discharge throughthe open end I3 of the screen are returned of course vthrough thepassage 39 to the classifier. 'I'his operation results in -a reductionof almost of the amount of finely ground mineral produced .in whichpractically all of the mineral is ground to minus three hundredtwenty-five mesh before it is delivered to flotation machines forconcentration. The reduction in the production lof unrecoverable slimesis of course greater since the production of slimes is a cumulativeprocess which is greatly aggravated by frequent regrinding. The improvedresults are of course most signiilcant in the reduction by over 50% ofmineral lost in waste waters. Aboutof the total mineral delivered to thegrinding mlllis recovered in the unit notation cell, the balance carriedin the overflow by the classifier is removed on subsequent treatment.

To improve the character of the froth in the flotation apparatus, a sandrelief passage is provided directly in line with the impeller dischargeto carry off heavy sands which tend to build up in a sand stratum beforeleaving the flotation cell. A sand stratum of this character occurs inthe upper portion of the cell and is made up of the heavier sandscarried upwardly but which before being carried awaycollect in a sandstra- A tum below the froth layer and intend to impair the quality ofthe froth level. The sand relief passage in the present case is shown inthe form oi a pipe 40 whose inlet end 4I is opposite the periphery ofthe impeller where the pulp currents obtainthelr maximum velocity. The,sand relief pipe leads to the tailings launder 33 but terminates at 42below the level of the overflow Weir 35. The dierence in liquid levelbetween the overflow weir and the discharge end 42 of the pipe producesa small hydraulic head which contributes to an increased flow throughpipe 40. The pipe is of a size sufficient to carry away aboutone-quarter of the heavy sands, that being suflicient to prevent aconcentrated sand stratum in the cell.

In very heavy ores, such for example as gold, large sizes of high gradeore V(which therefore have high specific gravity) may be too heavy to becarried by flotation. These may be removed by the use of a collectingpocket 44 at the bottomA of the cell which is here shown in the form ofa cone in which the heavy mineral may collect and be occasionallyremoved. The pulsating effect produced by the ribs on the under face ofthe impeller (see Fig. 4) aids in separating out heavy and oversizemineral. The cone is closed at its bottom by an appropriate valve hereshown in the form of a plug valve which may be opened from time to timeto permit the collected ore to fall out. In gold ores, for example, thevalue of the high grade ore thus collected is substantial.

Since in most instances the pulp feed is not sumciently dilute foriiotation machine operation, Water is generally added and if acollecting pocket be used on the cell, the water may be convenientlyadded at this point so that its upward flow tends to wash the oreandcarry up any smaller and lighterparticles of ore found trapped withthe heavy high grade ore. Such water may be introduced through pipe t5and its rate of ow controlled by valve 41.

In some installations a jig 43 may advantageously be interposed in thefeed line to take out tramp steel and large, heavy pieces of ore whichbecause of a defect in the screen or otherwise, invariably i'lnd theirway into the feed. The tramp steel is thereby prevented access to thecell and excessive abrasion of the rubber impeller and rubber celllining is avoided. In the absence of a jig, such heavy material would ofcourse be co1- lected in the pocket dit. The jig is preferably of aconventional hydraulic type and its details are unimportant here.

The eective incorporation of air in the pulp renders the apparatusadvantageous also in the cyanide process which requires an aerated pulpfor efficient operation. Minerals, such as copper sulphide, which arecyanicides, i. e. have a detrimental effect on the cyanide process, maybe concentrated in a froth on the pulp and this removed and preventedfrom interfering with the cyanidation. In the amalgamation process,coarse gold is removed in the collecting pocket t and such froth as maybe formed without the usual oil (oil being detrimental in theamalgamation process) is lilie- Wise removed.

In connection with the present illustrative construction, it should benoted that the pumping action of the impeller eliminates both the use ofauxiliary pumps to reelevate pulp and the loss of head room which wouldresult if the material traveled solely by gravity iiow. The loss of headoccurring from the grinding mill inlet to the bottom of the notationcell is more than made up by the action of the impeller which elevatesthe tailings discharge to a point (i. e. the weir overflow) where thetailings may dow by gravity back into the classifier. In someinstallations a greater gain in elevation than can be eected by a singlecell may be desired. In that case a plurality of cells each higher thanthe preceding one maybe placed in series, each elevating the pulp to thenext.

It should be understood of course that the economies above pointedoutdonot result merely from the use of a concentrating unit at thedischarge end of the grinding mill but the operation of the grindingmill so as to deliver a coarse mesh material to the unit and the use vofa junit capable of handling heavy coarse mesh material ore. Obviously aunit which could not handle coarse heavy particles would beinappropriate in the system since it would eventually clog up no matterhow small the percentage of heavy particles. VIt should be understoodthat the present otation apparatus is capable not only of floatingcoarse particles but coarse particles of heavy minerals. Obviously the ta :u size of the particles (asl 3 suming them to be generally ofspherical shape and not aky in character) depends upon the specicgravity of the mineral. The present apparatus makes it possible to iioatnot only coarse particles but coarse particles of heavy minerals v suchas gold, lead, etc.

Obviously the invention is not limited to the details of theillustrative construction since these may be variously modified.Moreover it is not in-r dispensable that all features ofthe invention beused conjointly since various features maybe used to advantage indifferent combinations and subcombinations. y

Having described our invention, we claim: 1. Apparatus oi the characterdescribed comprising in combination a pulp cell having adjacent itsbottom a rotary impeller carried on a vertical shaft, means for feedingpulp to the cell and discharging it in the cell at a point over theimpeller, said impeller having a closed bottom so that all pulpdelivered to the impeller must pass through and be acted upon therebybefore reaching' the CFI body of the pulp in the cell, means for feedingair to the impeller to be incorporated thereby in the pulp. said cellhaving a pocket in its bottom below and closely adjacent said impellerto receive oversize particles of ore too heavy to be elevated by thepulp currents generated by said impeller, said impeller having vanes onits under surface to develop a pulsating to carry entrapped sands fromsaid pocket. l

2. Mineral concentrating apparatus comprising in combination grindingapparatus, a flotation unit and a classifier in closed circuit, thegrinder being arranged to feed the ore pulp by gravity into the notationunit, said unit having a tailings overow substantially above theclassifier and having a rotary impeller which aerates the pulp andcreates upward currents of sufdcient velocity to carry the tailings overthe tailings discharge but without disturbing the froth layer at the topof the unit, a conduit for carrying the tailings from the dotation unitby gravity into the classier, and a san 'relief passage leading upwardlyfrom the imp ller to a point above the classiiier but below the tailingsoverow to provide a hydrostatic head toassist in carrying away sands tooheavy to pass over the tailings overdow.

3. Mineral concentrating apparatus comprising in combination oregrinding apparatus adapted to deliver ore ground to minus one-quarterinchmesh, a notation cell adapted to receive said ground ore from saidgrinder, said cell having therein a pulp inlet and a tailings overflow,a ro-l tary impeller to agitate the pulp and create Vupwardly directedcurrents `which elevate the tailings to said tailings overflow, aclassifier in closed circuit with said grinder and :dotation cell forretg coarse mineral to said grinding apparatus for regrinding andarranged with its lower end below the point of tailings discharge fromsaid cell, a tailings conduit for receiving the tailings from said celland leading to said classiiier whereby said tailings may ow by gravityinto said classifier, said dotation cell having an upwardly extendingconduit leading directly to the level of the tailings conduit anddischarging into said tailings conduit below the level of said tailingsoverow so that coarse sands may be returned by gravity to said classier.e

i. Mineral concentrating apparatus comprising in combination oregrinding apparatus adapted to deliver ore ground to minus one-quarterinch mesh, a notation cell having a pulp inlet, a chute y to receivesaid ground ore from said grinder and point substantially above the pulpinlet, a classifier in closed circuit with said grinder and fiotationcell and arranged with its lower end below the point of tailingsdischarge from said cell, a tailings conduit for receiving the tailingsfrom said c ell and leading by gravity to said classifier, saidclassifier having classifying mechanism therein which in its classifyingoperation elevates the heavy mineral to a point above the level oi theinlet into said grinding apparatus, and a conduit for carrying suchheavy mineral by gravity from said classifier to said grindingapparatus.

5. Mineral concentrating apparatus comprising in combination oregrinding apparatus adapted to deliver ore ground to minus one-quarterinch mesh, a flotation cell having a pulp inlet, a chute to receive saidground ore from said grinder, and to convey the same to said pulp inlet,a rotary impeller to agitate the pulp and create upwardly directedcurrents which elevate the tailings to a discharge point substantiallyabove the pulp inlet, a classifier having its inlet and heavy mineraldischarge in closed circuit with said flotation cell and grindingapparatus and arranged with its inlet end below the point of tailingsdischarge from said cell, said classifier being adapted to discharge itsfines out of said circuit for subsequent concentration, a tailingsconduit leading from said cell to said classifier inlet whereby saidtailings may fiow by gravity from said cell into said'classifier, saidclassifier being adapted to elevate the heavier and larger particles ofore in separating the same from the fine particles to a point above theinlet to the grinding apparatus, and a conduit for conveying saidheavier and larger particles from said classifier and discharging thesame into said grinding apparatus.

6. Mineral concentrating apparatus comprising in combination a flotationcell having an inlet and a tailings overflow above the level of saidinlet, a rotary impeller in said cell adapted to 4 create upwardlydirected currents of pulp of sumclent velocity to carry the tailingsover said tailings overfiow but without disturbingthe froth layer at thetop of the cell, a conduit for carrying away the tailings from saidtailings overflow, and a. sand relief passage leading upwardly from apoint adjacent said impeller directly to said conduit and discharginginto said conduit at a point below the level of said tailings overflow,thereby to create a hydrostatic head which assists in carrying sandsthrough said sand relief passage which are too heavy to be carried oversaid tailings overflow.

7. Apparatus of the character described comprising in combination a pulpcell having a. pulp inlet, a tailings overflow substantially above thelevel of the pulp inlet, a rotary impeller adjacent ,the bottom of saidcell adapted to receive pulp from said pulp inlet and to agitate thesame to' incorporate air therein and to create upwardly travellingcurrents of pulp of suflicient velocity to carry tailings to saidtailings overflow, an air conduit leading to said impeller to supply airfor incorporation in said pulp, a launder for carrying away tailingsfrom said tailings overflow, and a.

sand relief passage opening into said cell `in position to receive heavysands 'thrown out by said l impeller and having an upwardly extendingportion discharging directly into said launder at a level lower. thansaid tailings overflow for relieving the' cell of sands too heavy topass over the tailings overflow.

8. Apparatus of the character described comprising. in combination aflotation cell, means for feeding pulp to said cell, an impeller in saidcell arranged between the pulp feeding means and the body of the cell soas to require all pulp to pass through said impeller before reaching thebody of thefcell, said impeller being constructed and arranged todevelop upwardly directed currents of pulp, means for feeding air to theimpeller to be incorporated thereby in the pulp, said cell having apocket directly below said impeller and arranged to receive oversizeparticles after'they have passed through the impeller and which are tooheavy to be elevated by the pulp currents generated by such impeller,said pulp feeding means being arranged relatively to said pocket so asto require the pulp to pass through discharge outlet for said pocket topermit periodic discharge of the oversize particles from said pocket. 1

9. Apparatus of the character described comprising in combination a pulpcell having a pulp inlet and a tailings overflow, a rotary impeller insaid cell adapted to receive pulp from said inlet and to agitate thesame to incorporate air therein and to create vupwardly travellingcurrents of pulp of sufficient velocity to carry tailings to saidtailings overflow, an air conduit leading to said impeller to supply airfor incorporation in said pulp, a launder for carrying away tailingsfrom said tailings overflow, and a sand relief passage opening into saidcell opposite the periphery of said impeller and having an up- Wardlyextending portion leading directly into said launder at a level lowerthan said tailings overflow but above the level of the impeller fordirectly conducting away sands too heavy to pass over the tailingsoverflow.

10. Mineral concentrating apparatus compris- Y ing in combination oregrinding apparatus adapted to deliver ore ground to minus one-quarterinch mesh and having meansl for separating and separately dischargingoversize particles, a flotation cell having an inlet, a chute to receivesaid ground ore from said grinder and to convey the same toA said inlet,a rotary impeller to agitate the pulp and create upwardly directedcurrents which elevate the tailings to a point substantially above thepulp inlet, a classifier in closed circuit with said grinder andflotation cell and arranged with itsinlet end below the point oftailings discharge from said cell, a tailings conduit for receiving thetailings from saidcell and leading to said classifier, said classifierhaving classifying mechanism therein which in its classifying operationelevates the heavy mineral to a point above the level of the inlet intosaid grinding apparatus, a conduit for carrying such,

JOHN J. DENNY. ARTHUR C. DAMAN.

